Recently, for addressing environmental issues and energy problems, an automobile that uses output from a secondary battery as the driving source and at least partially has an electrically driven device has received attention.
Such an electric automobile uses output from the secondary battery as the entire driving source, and is run by driving force of a motor. A so-called hybrid car system that concurrently uses a motor and an engine and a so-called idle stop system car proceed toward commercialization in some manufacturer. Here, the so-called idle stop system car means a car where idling is stopped at parking time and the electric power of the motor assists the engine power at a restart time
In the electric automobile, instead of a special battery such as a fuel cell or a sodium sulfur battery operated in a special high-temperature region, a lead acid storage battery, a nickel-hydrogen storage battery, or, recently, a lithium secondary battery including organic electrolyte is employed in a relatively many cases. That is because these batteries can be operated in a normal temperature region, and is safe, easy-to-handle, and economical.
While, the characteristic of a secondary battery and the reliability including the lifetime and safety largely depend on the battery and its environmental temperature, and affect the characteristic and reliability of the vehicle to which the battery is mounted.
It is preferable to place the battery in an environmental condition where ambient temperature is higher than 30° C. in view of the output power characteristic. When the ambient temperature decreases, the output power largely decreases comparing with that in the preferable temperature region and a traveling characteristic of the vehicle decreases.
In view of the lifetime characteristic of the battery, it is preferable that the ambient temperature is lower than 40° C. When the ambient temperature exceeds 40° C., the self-discharge increases. Especially, the lithium secondary battery remarkably depends on temperature, the output characteristic and safety thereof are apt to be affected by the ambient temperature.
When the lithium secondary battery is used for example, the energy obtained under the environment at 0° C. is 60% to 70% of the output energy at ambient temperature of 30° C. to 40° C., and the energy obtained at −20° C. is about 10%. When the lithium secondary battery is used or left for a long time at a higher ambient temperature of 60° C., the organic electrolyte from a safety valve dissipates, or the sealing mechanism breaks. These phenomena cause inconvenience in safety of the characteristic and reliability. The other normal-temperature-type batteries such as a lead acid storage battery and a nickel-hydrogen storage battery have a similar tendency more or less.
A conventional cooling mechanism such as a compressor has a complex mechanism and requires much energy. In the electric automobile, therefore, emphasis is generally laid on heat retaining property at a low temperature, and a configuration considering securement of a battery characteristic is employed. However, practical application to a high temperature environment is kept at a distance, and the general purpose property is apt to be restricted.
In a vehicle that uses output from a normal-temperature-type battery as the power supply and has an electrically driven system in any way, a design for optimizing the output from the battery during traveling especially in a low temperature environment is employed. For example, a battery storing box having an insulating function as high as possible is produced and temperature of the battery or in the battery storing box is controlled using various heat sources.
Japanese Patent Unexamined Publication No. H8-22845 (pages 3-7, FIG. 1 or the like), for example, discloses the following configurations:                a battery is surrounded by a double outer wall including a vacuum layer;        a combustion heater or the like is installed in a circulation route of radiator water, and a battery is heated or cooled using the heater; and        the temperature of the battery is controlled using a panel heater that is installed on a heat retaining member wall and has a positive temperature coefficient (PTC) device or a nichrome wire.Here, the PTC device is used as a heating mechanism and has resistance variation coefficient having a positive characteristic with respect to temperature.        
Japanese Patent Unexamined Publication No. 2003-7356 (pages 4-7, FIG. 1 or the like) discloses a mechanism where a thermal converting device having Peltier effect is disposed on a wall surface of a battery box made of vacuum heat insulating material, and heats and cools the battery in the battery box.
An electric automobile including an electrically driven device has a battery storing box, and controls environmental temperature of the battery and the battery storing box with any means. Furthermore, it is considered that an output characteristic of the battery is especially important for controlling the environmental temperature, and the battery storing box includes a heat retaining box having high heat retaining property that is obtained by employing heat insulating material having high heat insulation property.
It is conventionally known that a vacuum heat insulating material has high insulating effect as the heat insulating material. Various vacuum heat insulating materials having high practicality are developed, and each of the materials is formed of a core material and an exterior package such as plastic laminated film. Here, the core material is formed of the following materials:                a hollow body of polyurethane foam, glass, or a metal plate;        a hollow body including a resin molded body as the wall material;        powder or fiber such as glass wool or silica; or        continuous foam such as polyurethane foam.        
Japanese Patent Unexamined Publication No. 2001-317686 (pages 3-4, FIG. 1 or the like) discloses a new manufacturing method of heat insulating material using the core material and the plastic laminated film. In this manufacturing method, decompression and sealing are established by laminated film having thermally welded resin on mutually facing surfaces. Thus, spaces having lightweight and high heat insulation property can be formed in various forms, and the vacuum heat insulating material is easily applied to the battery storing box for an electric automobile. When the electric automobile is required to be applicable to widespread temperature environment and quality of the heat insulating material and the manufacturing technology are improved, however, a new issue becomes apparent related to high temperature control of the battery or the battery storing box.
The battery storing box having high insulating and heat-retaining property exerts a preferable insulating characteristic, especially in low temperature environment. However, the battery itself is a heating element having high heat capacity, and generates heat by charge or discharge. When high output is continued for a long time, temperatures in the battery and the battery storing box rapidly increase.
The temperature in the battery storing box, after rising to a high temperature, does not easily decrease because the inside has high insulating characteristic. The battery is therefore left in an undesired high temperature state. When the temperature in the using environment of the automobile becomes high and the heat retaining function becomes high, the heat retaining function works reversely and the battery storing box hardly releases heat. Therefore, even when the electric automobile stops, the high temperature state is kept for a long time. When the battery left in the high temperature state is discharged, the temperature increase accelerates and the temperature inside the battery storing box further increases.
When the battery is left in the high temperature state, a problem arises in the stability of the characteristic or securement of the safety of the battery. Especially, it is not preferable that the lithium secondary battery having organic electrolyte containing many vaporization components is left in the high temperature environment.
A conventional cooling mechanism using a compressor cannot be applied to an electric automobile during parking. A mechanism employing an electric compressor or a thermal converting device having Peltier effect consumes much energy, and is therefore inefficient.
For controlling temperatures in the battery and the battery storing box of the electric automobile, a new temperature controlling means capable of effectively avoiding danger at high temperature with less energy while keeping high heat retaining characteristic at low temperature is desired to be developed instead of the conventional cooling mechanism.
The present invention addresses the problems discussed above. The present invention provides a battery storing means capable of easily suppressing temperature increase in the battery storing section and the battery in high temperature environment without damaging the high heat retaining function required in low temperature environment.